Modified diamond particles

ABSTRACT

Modified diamond particles for use in chromatography with a desired functional group at the diamond surface, formed from reaction of hydroxyl groups at diamond surfaces with a reactive molecule.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/526,410, filed 18 Jun. 2012, which is a divisional of U.S. patentapplication Ser. No. 12/557,503, filed 10 Sep. 2009, which claimspriority from U.S. Provisional Patent Application 61/191,692, filed 10Sep. 2008, the disclosure of each of the foregoing applications ishereby incorporated by this reference.

BACKGROUND

Since the inception of modern chromatography, silica based stationaryphases have dominated the world of chemical separations. Unfortunately,silica has certain limitations. Under acidic conditions, silica tends tolose its functionality and under basic conditions it dissolves entirelyafter a matter of hours. Not until recently have alternatives to silicabeen available such as polymer based stationary phases. These tend toswell when exposed to organic solvents and are therefore not ideal forreversed-phase separations.

Chemists have worked around the limitations of available stationaryphases, but these workarounds often result in less than ideal outcomes.For instance, certain separations may need to occur under basic oracidic conditions because the analyte of interest may only be stableunder a certain pH range. It is would therefore be ideal to find a phasethat could perform a separation under extreme pHs that current phasescannot successfully do separations at.

Diamond has usually been assumed to be inert and relatively little hasbeen done to investigate the possibility of diamond as the basis for astationary phase. Nosterenko et al. has performed separations ofproteins using oxidized/cleaned diamond and Saini et al. has beensuccessful in coating the diamond surface with poly(allylamine). Thiscoated diamond was then used as a normal phase in Solid-phase Extraction(SPE). Saini's study also showed that his phase was extremely stableunder extreme pH conditions (from pH 0-pH 14) for 24 h. The SPE columnwas able to be reused many times and showed no signs of degradation. Italso performed in the same manner experiment after experiment and onlyrequired a flush with ethyl acetate in between uses.

These two groups have shown that separations can indeed be performedwith diamond as the basis for a stationary phase. Nesterenko's studylacked good resolution in it HPLC spectra and Saini's capacity was quitelow, but efforts are being made to remedy the capacity issue.

CITED REFERENCES

[1] US Patent 20050189279

[2] US Patent 20040118762

SUMMARY

A new phase is directly bonded to the diamond surface which has beenlargely hydroxyl terminated. In a specific example, diamond cleaned withpiranha solution is treated with lithium aluminum hydride (LAH). Thisreaction greatly increases the amount of hydroxyl groups on the diamondsurface. Since hydroxyl groups are reactive to various functionalgroups, this chemistry is exploited to attach ligands directly to thediamond surface. For example, isocyanates and acyl halides (primarily Brand CI) are reactive to the hydroxyl functional group and form urethaneand ester linkages respectively, that are directly bonded to the diamondsurface. (See FIG. 1)

Bases do have the ability to hydrolyze this linkage at the carbonylsite, so bulky groups (methyl, isopropyl, tert-butyl, phenyl etc.) canbe attached to the α-carbon of the ligand to sterically hinder thebinding site and prevent bases from accessing the partially negativecarbon. This should give this type of linkage greater stability in thepresence of acids and bases. The reusability and consistency of thecolumn is also expected to be similar to that of Saini's column and thischemistry can be applied to HPLC and SPE stationary phases.

An aspect is a method for preparing modified diamond particles for usein chromatography where hydroxyl groups at the diamond surfaces arereacted with a reactive molecule to introduce a desired functional groupat the diamond surface. An example is the reaction of Isocyanates andacyl halides with hydroxyl-terminated diamond to form HPLC/SPEstationary phases.

Another aspect is a method for preparing modified diamond particles foruse in chromatography where i) diamond particles are reacted with anoxidizing agent that introduces carboxyl groups at the surface of thediamond, ii) the carboxyl groups are reduced to primary alcohols, andiii) the primary alcohols are reacted with a reactive molecule tointroduce a desired functional group at the diamond surface.

The diamond particles of the present method can be used in any suitabletype of chromatography type. These include, for example, highperformance liquid chromatography (HPLC), ultra performance liquidchromatography (UPLC), solid phase extraction, electrochromatography,size-exclusion chromatography, ion chromatography, affinitychromatography.

The chromatography may be practiced at any suitable pressure, such asfor example, between 1000 psi and 15000 psi.

The diamond surface may be prepared by reducing the surface with asuitable reducing agent prior to reaction with the reactive molecule.Any suitable reducing agent is contemplated, such as, for example,lithium aluminum hydride.

The reactive function group may be any suitable functional group withthe desired reactivity, and may have attached to the reactive group analkyl group or aryl group. The alkyl group may have the form—(CH₂)_(n)CH₃, where n=0-25. The alkyl group may be branched orunbranched. The alkyl group may be partially or fully fluorinated, Thearyl group may have the form —C₆H₆. The aryl group may be partially orfully fluorinated.

Examples of the reactive functional groups include, one of or a mixtureof an alkyl isocyanate, an aryl isocyanate, an acid chloride with anaromatic group, an acid chloride with an alkyl group, an acid bromide,an alkyl halide, an aryl halide, a benzyl halide, a benzyl triflate, abenzyl mesylate, an alkyl mesylate, an alkyl tosylate, and an alkyltriflate.

The reactive functional group may contain more than one other group nearthe reactive site of the molecule, which provides steric hindrance forthe adsorbed species.

The reactive molecule may contain C—H bonds. The reactive molecule maycontain an electrophilic site and a leaving group.

Another aspect is a diamond particle for use in chromatographycontaining groups tethered to the diamond surface through ether, ester,or urethane linkages.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1: Scheme outlining basic chemistry for the formation of theisocyanate and acyl halide reacted diamond particles

FIG. 2: Spectra confirming the step by step synthesis of a carbamidelinked C₁₈ chain to the diamond surface

FIG. 3: Possible examples of the types of groups attached at theα-carbon site to increase sterics of the area in order to preventnucleophilic attack of a base at the carbonyl resulting in hydrolysis ofthe ether or urethane linkage.

DETAILED DESCRIPTION Example Experimental

Micro-diamond or diamond powder is treated with piranha solution (3:730% H₂O₂:conc. H₂SO₄) or any other suitable cleaning/etching solution.This cleans/etches the diamond surface and exposes the variousfunctional groups that naturally occur on the diamond surface. Thediamond must be dried thoroughly before the next step. This can beperformed by pulling argon through the powder or placing the powder in avacuum for many hours. The dryness can be verified by diffusereflectance infrared Fourier transform (DRIFT).

The cleaned dry diamond is then treated with 1M LiAlH₄ (LAH) suspendedin THF (or any other strongly reducing base) [1] for 24-68 h at roomtemperature (about 1 g diamond:5 mL LAH solution). Warning: LAH isextremely reactive to water. Use proper PPE. The reaction must beperformed under inert atmosphere (argon) and all glassware must be dry.The reaction is quenched by 1M HCl. This should be added very slowly dueto the reactivity of LAH with water and HCl. Once the reaction isquenched, the diamond is filtered over a fine fritted Buchner funnel andwashed with copious amounts of water. If white particles are present,rinse with more 1 M HCl to dissolved the reacted LAH. Once thoroughlyrinsed, the powder is dried completely. This gives hydroxyl terminateddiamond.

The reduced surface has been disclosed US patent [1], the reaction ofthe hydroxylated surface with various functional groups is notdisclosed. The present method is an improvement over the discloseddiamond-based chromatographic processes.

Another US patent [2] discloses powders “attached with hydrocarbon,amino, carboxylic acid, or sulfonic acid groups.” The present method isspecifically targeting the reaction of the hydroxylated surface with areactive molecule to introduce a desired functional group at the diamondsurface, such as, for example, reactive isocyanates and acyl halides,and this chemistry and these functional groups are not disclosed.

In a specific example, for this final step the hydroxyl terminateddiamond is then placed in a reaction vessel which is subsequentlyflushed with inert atmosphere. Then a reactive molecule is added to thepowder. For example, a desired isocyanate or acyl halide is added to thepowder (about 0.5 mL:1 g hydroxyl terminated diamond) then add enoughdry tetrahydrofuran (THF) or ether to completely dissolve the isocyanateor acyl halide. The reaction should then react for at least 18 h at roomtemperature. Filter the diamond over a fine fritted Buchner funnel andwash with a large amount of THF or ether to rinse away the unreactedisocyanate or acyl halide. Dry the powder completely. The powder is thensuspended in a solvent and pressed into an HPLC column.

Results and Discussion

Thus far, only octadecyl isocyanate has been reacted with the hydroxylterminated diamond. The evidence of the successive reactions can be seenin FIG. 2 by the DRIFT, ToF-SIMS and XPS spectra. There is a decrease inthe height of the alcohol peak (3500 cm⁻¹) seen in the octadecylisocyanate DRIFT spectrum as compared to the LAH spectrum. It is clearthat not all of the alcohol functional groups are reacted and this isattributed to the steric hindrance of the diamond surface. The 2° aminepeak at 3342.43 cm⁻¹, asymmetric and symmetric C—H stretches at 2920.95cm⁻¹ and 2848.21 cm⁻¹ and the carbonyl stretches at 1612.33 cm⁻¹ and1572.64 cm⁻¹ are indicative of successful bonding of octadecylisocyanate to the hydroxyl terminated surface as evidenced by theurethane (carbamide) linkage.

The ToF-SIMS data shows an increase of hydrocarbon fragments in thepositive ion spectra and a decrease of 0 (16 m/z) and OH (17 m/z)fragments in the negative ion spectra. This result is predicted becausefewer O and OH groups would be exposed on the diamond surface once theisocyanate group has reacted with the OH functional group. The XPSspectrum shows the presence of nitrogen which is absent from the piranhaand LAH treated diamond powders. The only source of nitrogen in thisexperiment is from the isocyanate group. This therefore further confirmsthe formation of the carbamide linkage on the diamond surface.

In another embodiment, an HPLC column is packed with 5 μm octadecylisocyanate reacted diamond powder. If non-porous diamond is used, fewplates are expected to be present on the column. This should be remediedby using porous diamond powder.

The chemistry of the present method is expected to work with variousisocyanates and acyl halides, including compounds with the disubstitutedα-carbons (see FIG. 3 for some examples). The acyl halide derivatives ofthese compounds would also be used including the tert-butyl group notshown in the figure. Other functional groups past the functionalizedα-carbon could include but are not limited to phenyl, naphthyl, chiral,perfluorinated, C₈, and C₁₀.

CONCLUSION

The chemistry for creating urethane (carbamide) linkages to the diamondsurface is straight forward and should prove useful in the creation ofdiamond-based HPLC and SPE stationary phases. The attachment ofoctadecyl isocyanate to the diamond surface has been verified and otherisocyanates/acyl halides should also react in a similar manner to thehydroxyl terminated diamond surface.

Once a diamond-based HPLC column is successfully created and used, theadded stability, reusability and consistency of these diamond columnswill exceed that of its similarly functionalize silica-basedcounterparts. This strength comes from the urethane and/or esterlinkages which bind the diamond and the functional group together. Thiswill result in greater stability at more extreme pHs and thedisubstituted α-carbon should help increase the stability further inbasic conditions.

While invention has been described with reference to certain specificembodiments and examples, it will be recognized by those skilled in theart that many variations are possible without departing from its scopeand spirit, and that any invention, as described by the claims, isintended to cover all changes and modifications that do not depart fromthe spirit of the invention.

What is claimed is:
 1. A chemical separation apparatus, comprising: astationary phase including a plurality of diamond surfaces, each of atleast some of the plurality of diamond surfaces including a modifiedsurface having at least one of an acyl halide derivative or anisocyanate derivative tethered to the modified surface through an esterlinkage or a urethane linkage respectively.
 2. The chemical separationapparatus of claim 1 wherein the at least one of the acyl halidederivative or the isocyanate derivative provides steric hindrance fromfurther reactions with at least one of the diamond surface, the esterlinkage, or the urethane linkage.
 3. The chemical separation apparatusof claim 1 wherein the acyl halide or the isocyanate derivative isformed from an acyl halide molecule or an isocyanate molecule having anelectrophilic site.
 4. The chemical separation apparatus of claim 1wherein the acyl halide derivative or the isocyanate derivatives isformed from an acyl halide or isocyanate molecule having a leavinggroup.
 5. The chemical separation apparatus of claim 1 wherein the acylhalide derivative or the isocyanate derivative is a reaction product ofone or more of alkyl isocyanate, aryl isocyanate, acid chloride witharomatic group, acid chloride with alkyl group, or acid bromide.
 6. Thechemical separation apparatus of claim 1 wherein the acyl halidederivative or the isocyanate derivative includes one of or more of alkylgroups or aryl groups.
 7. The chemical separation apparatus of claim 6wherein the acyl halide derivative or the isocyanate derivative includesan alkyl group with the formula —(CH₂)_(n)CH₃, where n=0-25.
 8. Thechemical separation apparatus of claim 6 wherein the acyl halidederivative or the isocyanate derivative includes an alkyl group that isbranched.
 9. The chemical separation apparatus of claim 8 wherein thealkyl group is branched after an α-carbon of the acyl halide orisocyanate derivatives.
 10. The chemical separation apparatus of claim 6wherein the acyl halide or isocyanate derivative is branched at anα-carbon thereof.
 11. The chemical separation apparatus of claim 6wherein the acyl halide derivative or the isocyanate derivative includean alkyl group that is partially or fully fluorinated.
 12. The chemicalseparation apparatus of claim 6 wherein the acyl halide derivative orthe isocyanate derivative includes an aryl group that is partially orfully fluorinated.
 13. The chemical separation apparatus of claim 1wherein the plurality of diamond particles are porous diamond particles.14. The chemical separation apparatus of claim 1 wherein the at leastone of the acyl halide derivative or the isocyanate derivative includesone or more functional groups near enough to the ester linkage or theurethane linkage effective to provide steric hindrance for furtherreactions at the diamond surface.
 15. The chemical separation apparatusof claim 1 wherein the chemical separation apparatus is configured as asolid phase extraction column.
 16. The chemical separation apparatus ofclaim 1 wherein the chemical separation apparatus is configured as achromatography column.
 17. The chemical separation apparatus of claim 16wherein the chromatography column is configured as a high-performanceliquid chromatography column, ultra-performance chromatography column, agel filtration column, an ion exchange column, or an affinity separationcolumn.
 18. A chemical separation apparatus, comprising: a stationaryphase including a plurality of diamond surfaces, each of at least someof the plurality of diamond surfaces including a modified surface havingat least one acyl halide derivative tethered to the modified surfacethrough an ester linkage.
 19. A method of separating an analyte, themethod comprising: disposing a solution containing an analyte in achemical separation apparatus, the chemical separation apparatusincluding a stationary phase including a plurality of diamond surfaces,each of at least some of the plurality of diamond surfaces including amodified surface having at least one of an acyl halide derivative or anisocyanate derivative tethered to the modified surface through an esterlinkage or a urethane linkage respectively; and separating the analytefrom the solution with the chemical separation apparatus.
 20. The methodof claim 19 wherein the at least one of the acyl halide derivative orthe isocyanate derivative provide steric hindrance from furtherreactions with at least one of the diamond surface, the ester linkage,or the urethane linkage.